(A nonwoven fabric is defined as an interlocking (fiber) network characterized by flexibility, porosity and integrity.) The individual fibers used to compose the nonwoven fabric may be synthetic, naturally occurring, or a combination of the two. The individual fibers may be mechanically, chemically, or thermally bonded to each other. Nonwovens are used commercially for a variety of applications including insulation, packaging, household wipes, surgical drapes, medical dressings, and in disposable articles such as diapers, adult incontinent products and sanitary napkins. (Tissue is a closely related material in which the individual fibers may or may not be chemically bonded to one another.)
In may of the aforementioned applications it is necessary to adhere the nonwoven or tissue to another substrate or component. (The second substrate may be another nonwoven, tissue, or an unrelated material.) A commonly employed technique to bond the assembly together is the use of a hot melt adhesive. Hot melt adhesives allow for cost and time efficient manufacturing since there is no evaporation step necessary as is the case for water based or solvent based adhesive systems. Suitable hot melt adhesives must possess excellent adhesion to the substrates involved. For nonwoven applications they must also possess good flexibility (or hand), no staining or bleed through, suitable viscosity, set speed and open time to function on commercial available equipment and finally, acceptable thermal aging properties.
(Recently a variety of nonwoven and tissue applications have been developed which require that the hot melt adhesive demonstrate appreciable water solubility, dispersibility or sensitivity.) In these situations the hot melt adhesive must provide a durable bond to the nonwoven or tissue until exposed to a predetermined condition (e.g., room temperature water), after which the adhesive would release from the substrate(s). This ambient water releasability is a particularly desirable property in the disposable market where flushability and/or degradeability are becoming critical.
(Such a water soluble, dispersible or sensitive composition would also find utility as a binder to chemically bond the nonwoven fibers together in the manufacture of the nonwoven fabric or tissue.) Such a thermoplastic, water sensitive binder would allow for high speed manufacturing and would produce a nonwoven or tissue which would disintegrate under a desired condition.